1. Field of the Invention
The present invention relates to a control device and a control method for an elevator of the type in which the operation of a plurality of cars running in the same shaft is controlled.
2. Description of the Related Art
An ordinary elevator system adopts a form in which one car serves in one shaft. In contrast to such an ordinary elevator system, there exists a one-shaft multi-car system in which a plurality of cars serve in one shaft, and various proposals have been made regarding such a multi-car system.
In the most typical form proposed, an ascent shaft, a descent shaft, and connection shafts connecting the terminal floors thereof form a shaft loop in which cars run (a circulation type running shaft), and a plurality of elevator cars run in this loop in a circulating manner. In such a multi-car system, a plurality of cars run in the same shaft.
In performing operation control in the case in which a plurality of cars run in the same shaft, attention must be paid to the following points. First, it is necessary to prevent the cars from colliding with each other. Further, when there is generated a blocked state, in which a succeeding car cannot run due to a preceding car being in a standby state, it is necessary to get rid of such a blocked state, thereby achieving an improvement in transportation efficiency.
Regarding the former point, that is, the prevention of collision, a control method is available according to which there is provided a block distance between a preceding car and a succeeding car, keeping the succeeding car off the preceding one by a distance not smaller than the block distance (see, for example, JP 3029168 (hereinafter referred to as Patent Document 1)). Regarding the latter point, that is, the achievement of an improvement in transportation efficiency, a control method is available according to which, when a car is about to pass a floor generating a landing call, an unbalance in the allocation of cars is evaluated to thereby make a judgment as to whether the car is to be stopped at that floor in response to the landing call or not (see, for example, Treatise D of the Japanese Electro-technical Committee, vol. 117, No. 7, pp. 815 to 822 (1997)(hereinafter referred to as Non-Patent Document 1)).
However, the above-mentioned prior-art techniques have the following problems. Patent Document 1 only describes a collision preventing method and mentions nothing about avoidance of a blocked state or achieving of an improvement in transportation efficiency. In Non-Patent Document 1, it is assumed that each car is run in the normal manner. This assumption, however, is considerably unrealistic in an actual system. For example, it would be necessary to run all the cars even during off-peak times such as at nighttime, resulting in considerable waste from the viewpoint of power consumption.
In a normal one-shaft-one-car system, the car responds to every call request unless a special operation is being conducted, and is left in a standby state with the door closed after the passengers have got off. However, if applied to a one-shaft-multi-car system, this concept would, as easily expected, lead to deterioration in transportation efficiency due to a blocked state. Thus, there are problems of how to realize an elevator operation in which cost efficiency is taken into account and of how to achieve an improvement in elevator transportation efficiency.